1. Field of the Invention
The present invention relates to a power supply device having a plurality of power storage devices connected in parallel. The present invention also relates to an electric vehicle that incorporates such power supply device.
2. Description of Related Art
A power supply device having a plurality of power storage devices connected in parallel is generally known. Such a power supply device achieves high capacity and high power by providing the plurality of power storage devices.
For each such power storage device, a current allowed to flow through the power storage device (hereinafter referred to as an “allowable current”) is established. If the current that flows through the power storage device exceeds the allowable current due to for example variation or change in the internal resistance of each power storage device, deterioration of the power storage device becomes accelerated.
Thus, technology was proposed in which a current that flows through each power storage device is controlled such that the current that flows through each power storage device does not exceed the allowable current. See e.g. Japanese Patent Laid-Open No. 2008-118790.
More precisely, the power supply device has a current distribution unit connected in series to the power storage device. The current distribution unit controls the current that flows through the power storage device by changing a resistance value of a resistance provided in the current distribution unit.
As described above, deterioration of the power storage device is accelerated when the current that flows through it exceeds the established allowable current due to for example variation or change in the internal resistance of the power storage device.
In addition, if the temperature of each power storage device varies largely due to its positional relationship and a difference in the heat release property of each power storage device, the degree of deterioration varies among the power storage devices. Since the life duration of the entire power supply device is determined by the life duration of the most deteriorated power storage device, if the degree of deterioration in each power storage device varies, the life duration of the power supply device is reduced.
In the above-described technology, while the current that flows through each power storage device is controlled such that it does not exceed the allowable current, variation in the temperature of each power storage device was not considered. In other words, in the above-described technology, shortening of the life duration of the power supply device is still caused by the temperature variation in each power storage device, even though allowable current flow is controlled.
Therefore, an object of the invention is to provide a power supply device and an electric vehicle incorporating the power supply device, which can reduce shortening of the life duration of the device as a whole by restraining the increased temperature and the varied temperature of each power storage device.